Download Lab 9 – A Repulsive Lab

North Carolina State University PY131 Lab Manual Lab 9 – A Repulsive Lab Lab 9 – A Repulsive Lab INTRODUCTION Each time you use your bankcard to withdraw money from a teller machine or buy lunch with your All-­‐Campus card, you are using technology based on magnetic properties. When you check a book out of the library, the magnetic strip in the binding is set so that it doesn't trip the alarm in the magnetic sensor in the doorway. Magnetic properties of materials vary widely in strength. At the higher end, in nature, scientists have detected magnetars, a special class of neutron star. Magnetism is due to the motion of electrons; electrons spin on their axes and rotate around the nucleus. The strong magnetic fields of these stars cause electrons to emit radiation that we can detect. At the lower end of the range, we have the simple refrigerator magnets that we are all familiar with. Magnets come in different shapes and sizes. We have bar magnets, cylindrical magnets, and horseshoe magnets, to name a few. A magnet has two poles; a north and a south pole. If you break a magnet into two pieces, you will get two magnets (of lesser strength), each with a north pole and a south pole. It is impossible to isolate a single pole, even if you break a magnet into very small pieces. A compass needle is a small magnetic needle that is free to swing on a pivot. In the absence of other magnetic materials in its vicinity, a compass needle will always point in the direction of the Earth’s magnetic field. The magnetic north is near the Earth’s geographic south and the magnetic south is near the Earth’s geographic north. So a freely swinging compass needle will come to rest along the Earth’s geographic north-­‐south line. Magnetic field lines are used to represent the magnetic field around a magnet. Arrows are used to indicate the direction of these field lines. By convention, field lines point away from the north pole and toward the south pole. The number of field lines per unit area in a region is a measure of the field strength. A strong field will have more lines in a given area as compared to a weaker field. A current in a wire will produce a magnetic field. The direction of this magnetic field can be found using what is known as the right-­‐hand rule. Circle your fingers around the wire with the thumb pointing in the direction of the current. The direction in which your fingers circle the wire gives the direction of the magnetic field. In this lab, you will investigate, by performing four short experiments, some of the properties of magnets. 1 North Carolina State University PY131 Lab Manual Lab 9 – A Repulsive Lab PROCEDURE Keep magnets in this lab away from magnetic strips on credit cards, student Ids, etc… Part A: Compass Points 1. Place a compass on the table away from any magnets (or other compasses). Determine the north-­‐south direction in relation to your classroom. The compass end pointing north is defined as the north-­‐seeking pole or simply the north pole of the magnet. Now bring the compass near a bar magnet. Which end of the red/green bar magnet appears to be a north magnetic pole? How can you tell? 2. On a large sheet of paper, arrange about eight or ten compasses in a circle as shown in figure 1. Note that the direction of the magnetic needles in this diagram is arbitrary. Place a single bar magnet in the center of this circle with its poles horizontal. What happens to the compass needles? Trace the magnet and indicate the north and south poles on the paper. Draw a sketch, on the worksheet, of the compass arrangement and indicate the Figure 1 direction of each compass needle. Use this result to draw the magnetic field lines around and through the magnet. Use arrows to indicate the direction of field lines. CHECKPOINT 1: HAVE YOUR TA CHECK YOUR WORK BEFORE PROCEEDING 3. Get a new piece of paper. Place two bar magnets, like poles facing and about an inch or two apart as shown in figure 2. Trace the outline of the two magnets on the paper. Place a compass in the space between the two poles. Which way does the compass needle point? Indicate the direction of the compass needle on the sheet of paper. Move the compass needle closer to the magnet on the left and then closer to the magnet on the Figure 2 right. Note what happens to the compass needle. Now move it up and down (along the dashed line shown in the figure), keeping the compass needle equidistant from the two magnets. Now what happens to the needle? Use the compass needle to 2 North Carolina State University PY131 Lab Manual Lab 9 – A Repulsive Lab investigate the magnetic field lines around these two magnets. Make a sketch, in the space provided on the worksheet, of the needle orientation for each of these compass positions. CHECKPOINT 2: HAVE YOUR TA CHECK YOUR WORK BEFORE PROCEEDING Part B: File it Away In Memory You are given 2 bar magnets, a plastic container with iron filings suspended in oil, and a tube of iron filings. Handle these magnets carefully. Do not let them hit against each other, as it will damage the magnets. 1. Using a clean sheet of paper (full size), center one bar magnet lengthwise UNDER the paper. Lightly sprinkle the iron filings onto the paper around the magnet. Be careful not to let the filings get on the actual magnets, they are difficult to get off. Sketch the pattern made by the iron filings, in the space provided on the worksheet. 2. Repeat step 1 with two bar magnets positioned with the like poles facing each other. Sketch the pattern on the worksheet. 3. Repeat step 2 with unlike poles facing each other. Sketch the pattern on the worksheet. 4. Give the container filled with iron filings (suspended in oil), a good shake. Move the cylindrical bar magnet around this container and see how it affects the suspended filings. If you orient the magnet side to side, what happens to the filings? If you orient the magnet up and down what happens to the filings? Where are the filings most concentrated? Why is this effect evident in oil and not on paper? Please return the iron filings to the bottle when you are finished. CHECKPOINT 3: HAVE YOUR TA CHECK YOUR WORK BEFORE PROCEEDING 3 North Carolina State University PY131 Lab Manual Lab 9 – A Repulsive Lab Part C: Magnets and Electricity You should have a coil of wire and a galvanometer. A galvanometer is a device, which registers a current or voltage. 1. Attach the coil to the galvanometer. Note what happens to the galvanometer needle. 2. Quickly insert one end of the bar magnet into the coil and pull it out quickly. Note what happens to the galvanometer needle (direction as well as the amount of deflection) as you do this. Enter your observations on the worksheet. 3. Repeat step 2 by altering the speed with which you insert and pull out the magnet. Enter your observations on the worksheet. 4. Insert the magnet and hold it still in the center of the coil. Note what happens to the galvanometer needle when you don’t move the magnet. Enter your observations on the worksheet. 5. Reverse the magnet and repeat step 2 by inserting the opposite end of the magnet into the coil. Again note the behavior of the galvanometer needle. Enter your observations on the worksheet. CHECKPOINT 4: HAVE YOUR TA CHECK YOUR WORK BEFORE PROCEEDING 6. Use the right hand rule for magnetic fields to predict which way the induced magnetic field is oriented. Use the drawings below. In the small circles around the single loops, indicate the direction of the magnetic field. Use  for a direction into the paper. Use  for a direction out of the paper. 4 North Carolina State University PY131 Lab Manual Lab 9 – A Repulsive Lab 7. On the two solenoids below, the electric current in the wires and the magnetic field lines (grey lines) are drawn, but the direction of the magnetic field lines has been omitted. Predict which direction these magnetic field lines will go by completing the lines with arrows. 8. Test your hypothesis with a compass. Was your prediction correct? CHECKPOINT 5: HAVE YOUR TA CHECK YOUR WORK BEFORE PROCEEDING Part D: Paperclips and Solids You are given some paperclips, two bar magnets, a compass and a plastic dish. 1. Hold one of the magnets near the Petri dish. Does the magnet attract or repel the petri dish? Now hold the magnet near a paperclip. Is the paper clip attracted to or repelled by the magnet? 2. Now hang one paperclip from the end of the magnet. Try hanging a second paperclip from the bottom of the first one. Explain why this is possible. 5 North Carolina State University PY131 Lab Manual Lab 9 – A Repulsive Lab 3. Gently take hold of the upper paper clip and remove the magnet. What happens to the bottom paperclip? Describe what affect the magnet had on the first paperclip. 4. Flip the magnet over and slowly bring the other end (that is, if you used the north end before, now use the south end) near the upper paperclip. What happens to the bottom clip? 5. Make sure that the Petri dish is about half-­‐full of water. Touch a paperclip to one end of a magnet then slowly suspend it in the Petri dish. This is easiest if you hold the paperclip by the long edges and lower your fingertips into the water before releasing it. Once the paperclip is floating on the water, bring one end of the magnet near the Petri dish. Describe how the paperclip behaves. 6. Now bring the other end of the magnet near the dish. Describe how the paperclip behaves. 7. Finally move all other magnets away from the dish. How does the paperclip align itself? Compare this to the compass. What can you conclude about the paperclip after it has been in contact with a magnet? CHECKPOINT 6: HAVE YOUR TA CHECK YOUR WORK BEFORE PROCEEDING 6 North Carolina State University PY131 Lab Manual Lab 9 – A Repulsive Lab MAGNETS – WORKSHEET Part A: Compass Points 1. Sketch of magnetic field lines in the region of a single bar magnet. CHECKPOINT 1 2. Sketch of magnetic field lines in the region of a two bar magnets with like poles facing each other. CHECKPOINT 2 7 North Carolina State University PY131 Lab Manual Lab 9 – A Repulsive Lab Part B: File it Away In Memory 1. Sketch the pattern made by the iron filings and one magnet, in the space provided below. 2. Sketch the pattern made by the iron filings and two magnets with like poles facing, in the space provided below. 3. Sketch the pattern made by the iron filings and two magnets with unlike poles facing, in the space provided below. Iron filings in liquid 4. If you orient the magnet side to side near the cylinder, what happens to the filings? 8 North Carolina State University PY131 Lab Manual Lab 9 – A Repulsive Lab 5. If you orient the magnet up and down what happens to the filings? 6. Why do more filings stick to the bottom pole? 7. Where are the filings most concentrated? Why is this effect evident in oil and not on paper? CHECKPOINT 3 Part C: Magnets and Electricity 1. Why does the scale read zero when you connect the coil of wire to the galvanometer? 2. What happens to the galvanometer needle when you quickly insert one end of the bar magnet into the coil and pull it out quickly? 3. What happens to the galvanometer needle when you change the speed with which you insert and pull out the magnet? 9 North Carolina State University PY131 Lab Manual Lab 9 – A Repulsive Lab 4. What happens to the galvanometer needle when you hold the magnet still in the center of the coil? 5. What happens to the galvanometer needle when you reverse the magnet and repeat step 2 by inserting the opposite end of the magnet into the coil? CHECKPOINT 4 6. In the small circles around the single loops, in the drawing below, predict and indicate the direction of the magnetic field. Use the right hand rule to do this. Use  for a direction into the paper. Use  for a direction out of the paper. 10 North Carolina State University PY131 Lab Manual Lab 9 – A Repulsive Lab 7. On the two solenoids below, the electric current in the wires and the magnetic field lines are drawn, but the direction of the magnetic field lines has been omitted. Predict which direction these magnetic field lines will go by completing the lines with arrows. CHECKPOINT 5: Part D: Paperclips and Solids 1. Did the magnet attract or repel the Petri dish? 2. Was the paper clip attracted to or repelled by the magnet? 3. Why were you able to hang a second paper clip from the end of the first one? 11 North Carolina State University PY131 Lab Manual Lab 9 – A Repulsive Lab 4. What happened to the bottom paperclip when you removed the magnet from the top paperclip? Describe what affect the magnet had on the first paperclip. 5. What happened to the bottom clip when you flipped the magnet over and slowly brought it near the upper paperclip? 6. Describe what happened to the paperclip in the water, when you brought the magnet close to it. 7. Describe what happened to the paperclip when you brought the other end of the magnet near the dish. 8. Once you removed all the magnets away from the dish, how did the paperclip align itself? Compare this to the compass. What can you conclude about the paperclip after it has been in contact with a magnet? CHECKPOINT 6: 12